The measurement of specific gravity of a liquid specimen is employed in a wide variety of technical fields. The measurement of specific gravity of urine is one of the important items of measurement in the field of clinical chemistry. Physical method for measurement using liquid gravimeters, urine gravimeters, pycnometers, refractometers,osmometers,etc. were usually employed for measuring the specific gravity of urine. The instruments used by these methods were, however, expensive and fragile, and their handling called for the utmost care. Moreover, the instruments called for occasional maintenance including cleaning and calibration. Thus, the measurement by any of these physical methods took a great deal of labor and time.
Simpler physical methods for measurement have been proposed. For example, Japanese Patent Application Laid-open No. 120843/1984 discloses a sheet for gravimetric examination formed from a porous resinous material, but a method employing this sheet calls for the strict determination by a spectrophotometer or refractometer of the transmission or refractive index of the sheet impregnated with a liquid to be examined, such as urine. Japanese Patent Application Laid-open No. 112251/1984 discloses a piece for the gravimetric measurement of urine having a gravimetric measuring chamber which holds a plurality of beads differing from one another is specific gravity, but it is too complicated in construction to be easily manufactured.
In the field of clinical chemistry methods relying upon colorimetric analysis by test pieces are employed for carrying out an assay for constituents in a specimen of body fluids, such as urine, at a low cost in a simple and quick operation. The methods relying upon colorimetric analysis are easy to understand and carry out with few errors, insofar as variations in color can be visually recognized. The results are easy to obtain visually, or by a simple device such as a color analyzer. Methods relying upon colorimetric analysis by test pieces for determining the ionic strength, or specific gravity of a liquid specimen have recently been proposed in, for example, Japanese Patent Publication No. 12858/1987, Japanese Patent Laid-open Nos. 160739/1984, 21064/1981, 66451/1990 and 95462/1987, and Japanese Patent Publication No. 46374/1985.
The known method for the colorimetric determination of the ionic strength, or specific gravity of a liquid specimen, as disclosed in the publications referred to above, employed test pieces prepared from, or by using, an electrolytic polymer, a chelate forming agent, a pH buffer agent, a pH indicator, a highly absorbent resin, a microcapsule, etc. It has, however, been difficult to carry out an accurate determination by any of the known methods, since the results thereof are easily affected by the pH or temperature of the liquid specimen, the length of time employed for the determination, etc. Moreover, many of the test pieces employed by those methods are generally difficult to prepare.
This invention is intended for overcoming the drawbacks of the prior art as above pointed out. It is an object of this invention to provide a composition which enables the measurement of ionic strength, or specific gravity of a liquid specimen to be carried out easily, quickly and accurately without being influenced by the characteristics of the specimen, such as its pH and temperature, and a test piece which is easy to prepare by using the composition.